High intake of processed meat may increase the risk of developing type-2 diabetes by 40 per cent, according to a new meta-analysis from Norway and the US.

Data from 12 cohort studies showed that high intakes of all types of meat were associated with a 17 per cent increase in the risk of type-2 diabetes, while similar risk increases were also noted for high intakes of red meat.

The study, published in the journal Diabetologia, adds to an ever increasing list of bad news for red and processed meat, following previous studies from the US National Cancer Institute (NCI) that reported high intakes of red and processed meats may raise the risk of lung and colorectal cancer by up to 20 per cent.

The World Cancer Research Fund published a report in 2007 that directly linked diet to cancer, with alcohol and red and processed meats posing particular risks.

Earlier this year, the same authors published similar findings from a study with half a million people, noting that that increased consumption of red and processed meat may have a modestly increased risk of death from all causes and also from cancer or heart disease (Archives of Internal Medicine, Vol 169, pp. 562-571).

The Archives study was described by Barry Popkin from the University of North Carolina as “excellent” in an accompanying editorial. Popkin added that the results “reiterate the concerns echoed in other major reviews and studies on the adverse effects of excessive meat intake”.

The new meta-analysis, led by Dagfinn Aune from the University of Oslo, sought to iron out the inconsistencies from previous studies which found both positive and negative associations between meat consumption and the risk of type-2 diabetes.

Of the 12 cohort studies pooled, the overall data suggested the high intake of total meat increased the risk of diabetes by 17 per cent, while red meat and processed meat were associated with 21 and 41 per cent increases in diabetes risk.

“These results suggest that meat consumption increases the risk of type 2 diabetes,” said the researcher. “However, the possibility that residual confounding could explain this association cannot be excluded,” they concluded.

A direct mechanistic study of how meat may affect diabetes risk has not been performed. However, an earlier study from Harvard University suggested several “possible biologically adverse effects of components in red and processed meats”, including saturated fatty acids and cholesterol. However, their study
(Diabetologia, 2006, Vol. 49, pp. 2604-13) failed to find an association between these components.

Another possibility is the effect of nitrites, frequently used as preservatives in processed meats. “Nitrosamines can be formed by the interaction of amino compounds with nitrites present either in the stomach or within the food product,” they explained. “They have been linked to beta cell toxicity. In addition, low doses of the nitrosamine streptozotocin were found to induce type 2 diabetes in animal models,” they added.

The possible effects of “residual confounding” and uncertainty over the possible mechanism show that more research is clearly needed in this area.